The 14‐3‐3 Proteins Encoded by the BMH1 and BMH2 Genes are Essential in the Yeast Saccharomyces cerevisiae and Can be Replaced by a Plant Homologue

Abstract

The 14‐3‐3 proteins comprise a family of highly conserved acidic proteins. Several activities have been ascribed to these proteins, including activation of tyrosine and tryptophan hydroxylases in the presence of calcium/calmodulin‐dependent protein kinase II, regulation of protein kinase C, phospholipase A2 activity, stimulation of exocytosis and activation of bacterial exoenzyme S (ExoS) during ADP‐ribosy‐lation of host proteins. In addition, a plant 14‐3‐3 protein is present in a G‐box DNA/protein‐binding complex. Previously, we isolated the BMH1 gene from Saccharomyces cerevisiae encoding a putative 14‐3‐3 protein. Using the polymerase chain reaction method, we have isolated a second yeast gene encoding a 14‐3‐3 protein (BMH2). While disruption of either BMH1 or BMH2 alone had little effect, it was impossible to obtain viable cells with both genes disrupted. The cDNA encoding a plant 14‐3‐3 protein under the control of the inducible GAL1 promoter complemented the double disruption. Transfer of the complemented double disruptant to a medium with glucose resulted in the appearance of a high percentage of large budded cells. After prolonged incubation, these cells became enlarged with irregular buds and chains of cells defective in cell‐cell separation became visible. These results suggest an essential role of the 14‐3‐3 proteins, possibly at a later stage of the yeast cell cycle.

The Candida albicans 14‐3‐3 gene, BMH1, is essential for growth

“…A wide variety of regulatory functions are attributed to the 14-3-3 proteins, which in many cases are due to their ability to bind phosphoserines (Muslin et al, 1996). While seven isoforms have been identified in mammalian cells, only two 14-3-3 proteins are present in Saccharomyces cerevisiae: BMH1, BMH2 (Gelperin et al, 1995;van Hemert et al, 2001;van Heusden et al, 1992van Heusden et al, , 1995 and Sz. pombe: RAD24, RAD25 (Ford et al, 1994).…”

Yeast 14‐3‐3 proteins

“…33 Although the S. cerevisiae 14-3-3 proteins can be phosphorylated in vitro by mammalian kinases, in vivo phosphorylation has not been reported. 12 A bmh1 bmh2 disruption is lethal in most laboratory strains, 43 but not in S1288-derived strains. 34 A bmh1 bmh2 disruption in the latter strain results in increased sensitivity to environmental stresses such as heat, high osmolarity and caffeine.…”

“…The two S. cerevisiae 14-3-3 proteins, encoded by BMH1 and BMH2, 17,43,45 are more than 60% identical to the mammalian e isoform. Bmh1p and Bmh2p are 91% identical and 97% identical, respectively, over the first 250 residues, therefore any isoform-specific function probably resides in the divergent C-termini.…”

“…In other strains, a conditional lethal mutant has a highly increased percentage of large budded cells under restrictive conditions. 43 After prolonged growth under restrictive conditions, chains of cells and cells with abnormal bud morphology are formed. Many of these cells lack DAPI-stainable nuclei but contain small spots instead, suggesting a disturbed nuclear organization or continued chromosome segregation.…”

“…Many of these cells lack DAPI-stainable nuclei but contain small spots instead, suggesting a disturbed nuclear organization or continued chromosome segregation. 43 This implies a role for the yeast 14-3-3 proteins in regulating mitosis and/or cell-cell separation.…”